Knee osteoarthritis (OA) causes pain and long-term disability and costs the US more than $65 billion per year. The impact will increase as the population ages. In addition to inconsistent effectiveness, current treatments such as nonsteroidal anti-inflammatory drugs, knee replacement, and physical therapy may be expensive, cause serious adverse effects, reduce physical function, and fail to improve mental well-being. Finding effective treatments to maintain function and quality of life in OA patients is one of the national priorities identified this year by the Institute of Medicine. Previous research has demonstrated that Tai Chi, an increasingly popular complementary and alternative therapy with both mind and body components, can improve physical and mental health;it can increase muscle strength, balance, and flexibility and can improve quality of life. However, no clinical trials have demonstrated its clinical effectiveness compared to a standard therapeutic regimen of physical therapy (PT) or its cost effectiveness in the healthcare marketplace. Therefore, we propose to conduct the first comparative effectiveness and cost-effectiveness trial of Tai Chi vs. PT in a large symptomatic knee OA population. We aim to demonstrate that, compared to standard PT, Tai Chi is a more cost-effective intervention for managing pain and reducing the functional limitations that impact quality of life for millions of individuals with knee OA. We believe that our work will convince the clinical community to implement Tai Chi as a first-line treatment for this crippling disease. To achieve this goal, we will conduct a single-blind, randomized, controlled trial of Tai Chi vs. PT in 180 patients who meet the American College of Rheumatology criteria for Knee OA. Patients will be randomized to 12 weeks of treatment with Tai Chi (2x/week) or Standard PT (2x/week for 6 weeks, followed by 6 weeks of rigorous supervised home exercise) with 24 and 52 week follow-ups. We aim to show that: 1) Tai Chi reduces knee pain more effectively than a standard regimen of PT (using the Western Ontario and McMaster University Index [WOMAC] pain subscale);2) Tai Chi improves functional capacity (WOMAC function subscale, and chair-stand performance), muscle strength, knee joint proprioception, health related quality of life (SF36), and psychosocial functioning (mood, stress, self-efficacy and social support measures) more effectively and for longer periods than PT;and 3) Tai Chi decreases healthcare utilization and thus reduces costs as compared with a standard regimen of PT. Successful completion of the proposed study will demonstrate that Tai Chi is a simple, inexpensive, effective, durable treatment for a major disabling disease with great social and economic costs. PUBLIC HEALTH RELEVANCE: Knee Osteoarthritis (Knee OA) is the most common musculoskeletal disorder in the world, with no currently proven disease-modifying medical remedies. Tai Chi offers a novel, logistically feasible exercise regimen and a complementary mind-body approach to manage pain and enhance physical and mental health and wellness in patients with Knee OA. Successful completion of the proposed study will demonstrate that Tai Chi is a simple, inexpensive, effective, durable treatment for a major disabling disease with great social and economic costs.